The present invention relates to a liquid crystal element (for example, a liquid crystal display element or liquid crystal display) including a plurality of bases each having a liquid crystal orientation film, wherein the surface sides, on which the liquid crystal orientation films are formed, of the adjacent two pieces of the bases are opposed to each other with a specific gap put therebetween and a liquid crystal is arranged in the gap, and to a method of manufacturing the liquid crystal element.
A liquid crystal display (LCD) using a liquid crystal as a display means has advantages in low power consumption, thin structure, and light weight. Such a liquid crystal display having the above advantages has come to be applied to a watch, electronic calculator, computer display, and television (TV) set.
Studies have been actively made to employ a ferroelectric liquid crystal (FLC) as the liquid crystal used for LCDs. The FLC was synthesized by R. B. Meyer in 1975 and a surface stabilized ferroelectric liquid crystal enabling domain inversion by an applied electric field was invented by N. A, Clark and S. T. Lagerwall in 1980. The FLC, whose molecules have permanent dipole moments in the directions perpendicular to major axes of the molecules, exhibits spontaneous polarization, and therefore, it is switchable by an applied electric field. A FLC display using the FLC mainly has the following excellent features (1) to (3):
(1) The switching speed is in the order of .mu.s which is as high as about 1,000 times that of a TN (Twisted Nematic) liquid crystal display. That is to say, the FLC display is excellent in high-speed responsiveness. PA1 (2) The molecule array has basically no twisted structure. That is to say, the FLC display has less viewing angle-dependence. PA1 (3) Even if a power supply is turned off, an image is held. That is to say, the FLC display has a feature of storing an image, so that it enables simple matrix drive even for 1,000 or more scanning lines capable of meeting the requirement of high precision display.
Accordingly, the FLC display is expected to realize performances such as higher precision, lower cost, and larger screen.
With respect to the ferroelectric liquid crystal element (for example, surface stabilized ferroelectric liquid crystal element), as shown in FIG. 25, the orientation of liquid crystal molecules M is switched between states 1 and 2 when an external electric field E (Ps: spontaneous polarization) is applied to the liquid crystal element. When the liquid crystal element is arranged between crossed-sheet polarizers, a change in orientation of liquid crystal molecules is converted into a change in light transmittance. To be more specific, as shown in FIG. 26, the transmittance is rapidly changed from 0% to 100% at a threshold voltage V.sub.th.
Since the ferroelectric liquid crystal display using a bistable mode exhibits only two stable states as described above, it is difficult to realize gradation display by controlling an applied voltage like the TN liquid crystal display.
To be more specific, the ferroelectric liquid crystal display element is difficult to realize gradation display by controlling an applied voltage because the transmission light is modulated such that the quantity of transmission light is rapidly changed. To cope with such an inconvenience, there has been proposed a method (area gradation method) of realizing gradation display by adjusting an image with the aid of additionally provided sub-pixels. The method, however, is disadvantageous in that since the gradation display is not performed in one pixel, it becomes insufficient or raises the cost if the size of one pixel is very small, for example, in the case where the liquid crystal element is used as a light modulation element.
To solve such a problem, there has been invented a technique of realizing digital gradation display while keeping a high contrast in the case of using a spatial light modulation element of a so-called ON-OFF type in which either of two states (transmission or non-transmission of light, or reflection or non-reflection of light) is selected, like the ferroelectric liquid crystal display element.
To be more specific, the above-described display technique is intended to display, in principal, gradations capable of producing an illusion of a continuous image for viewers by combining a field sequential method using a spatial light modulation element for selecting either of two states (transmission or non-transmission of light, or reflection or non-reflection of light) with modulation of the intensity of light supplied from a light source. This technique has been disclosed by the present applicant (Japanese Patent Laid-open Nos. Hei 5-347576 and Hei 7-212686).
For a reflection type light modulation element using a ferroelectric liquid crystal, a reflection layer allowing light supplied from a light source to be reflected therefrom, a ferroelectric liquid crystal layer for effecting light modulation, and a counter electrode for driving a ferroelectric liquid crystal are provided on a drive layer.
In the case of using a light source having one kind of light intensity, to display eight bits (256 levels) of gradations, the time (16.7 ms) for one frame must be simply time-divided into parts equivalent to eight bits (256 levels), that is, 0 to 255 steps, and accordingly, the ferroelectric liquid crystal must be perfectly driven at about 65.5 .mu.s/line. To display ten bits of gradations, the ferroelectric liquid crystal must be perfectly driven at about 16.3 .mu.s/line. From the viewpoint of the response speed of the present ferroelectric liquid crystal, it is difficult to realize the above drive speed. In other words, to realize the above drive speed, an applied electric field must be set at a high value.
The drive speed of the ferroelectric liquid crystal, however, can be made significantly larger by use of a light source capable of modulating the light intensity. If the light source is capable of modulating the light intensity in steps equivalent to eight bits (or ten bits) as shown in FIG. 27, the ferroelectric liquid crystal may be driven at about 2.08 ms/line (or 1.67 ms/line) for displaying eight bits (or ten bits) of gradations. Such a drive speed of the ferroelectric liquid crystal can be practically realized from the viewpoint of the response speed of the ferroelectric liquid crystal. Here, an image composed of one gradation bit is referred to as "bit plane", and the display time thereof is referred to as "bit plane time". For example, as shown in FIG. 27, if eight bits of gradations are displayed, the number of bit planes is eight and the sum of the eight bit planes constitutes one frame.
Recently, with advance of a digital display element typically in the field of plasma display panel, it is required to realize a high quality image. It has been reported that eight to ten bits of gradations are sufficient for digital gradation display but are insufficient for realizing a high quality image.
This is because eight to ten bits of gradations ensure sufficiently high image quality upon display of a static image but cause a problem associated with a pseudo contour upon display of a dynamic image.
The pseudo contour results from the fact that the divided bit plane display time becomes longer upon field sequential (time-division) drive. When the eyes of a viewer follows a light emission point, the retinas of the eyes receive an improper stimulus because a time deviation of the light emission pattern is converted into a spatial deviation thereof. This phenomenon is the pseudo contour. It has been already proposed by the present inventor to improve the pseudo contour by applying the bit plane division method to a light modulator using a ferroelectric liquid crystal (Japanese Patent Laid-open No. Hei 7-212686).
In this case, the problem associated with the pseudo contour can be solved by making infinitely shorter the bit plane time; however, from the viewpoint of the device structure, power consumption, and data transfer rate to a light bulb, it may be desirable to set one bit plane time at 100 .mu.s or more. Also, in terms of the response time of a ferroelectric liquid crystal and the drive voltage utilizing an active element, the time until completion of the switching of the liquid crystal may be set at 50 .mu.s and the one frame may be set at 36 bit planes.times.three primary colors.
It may be of course desirable to make the drive voltage of a liquid crystal as small as possible. The reduction in drive voltage is effective to omit a high withstand voltage transistor of a silicon VLSI circuit can be omitted. In consideration of the technical level of the present VLSI, it is required to set the drive voltage of the liquid crystal at 3 V or less.
The liquid crystal material requires various improvements, for example, extension of the usable temperature range in addition to the reduction in threshold voltage value associated with the above-described reduced drive voltage, and it may be considered that the reduction in threshold voltage value cannot be sufficiently achieved only by improving the liquid crystal material.
Since the gradation is controlled only using two values (white and black), the stability of transmittance becomes important. In particular, the temperature of the liquid crystal during display, which is changed depending on the environmental temperature in an operational room or the heat generation of a drive circuit, exerts an effect on transmittance, and consequently, it is essential to reduce the temperature-dependence on transmittance.
Further, it has been recognized that a ferroelectric liquid crystal light bulb exhibits a hysteresis phenomenon. To be more specific, not only the white or black having been displayed at the last bit plane but also the white or black having been displayed at the bit plane preceding the present one by several tens of bits, exerts an effect on the display of the present bit plane. Concretely, even if the display at the last bit plane is black, the color of the present bit plane is not determined into white or black because it is affected by the display color (white or black) at the bit plane before the last one. Such a phenomenon significantly appears in the ferroelectric liquid crystal having a larger difference between the full cone angle and memory cone angle.